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result(s) for
"Mass transfer"
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Inertially enhanced mass transport using 3D-printed porous flow-through electrodes with periodic lattice structures
Electrochemical reactors utilizing flow-through electrodes (FTEs) provide an attractive path toward the efficient utilization of electrical energy, but their commercial viability and ultimate adoption hinge on attaining high currents to drive productivity and cost competitiveness. Conventional FTEs composed of random, porous media provide limited opportunity for architectural control and engineering of microscale transport. Alternatively, the design freedom engendered by additively manufacturing FTEs yields additional opportunities to further drive performance via flow engineering. Through experiment and validated continuum computation we analyze the mass transfer in three-dimensional (3D)–printed porous FTEs with periodic lattice structures and show that, in contrast to conventional electrodes, the mesoscopic length scales in 3D-printed electrodes lead to an increase in the mass correlation exponent as inertial flow effects dominate. The inertially enhanced mass transport yields mass transfer coefficients that exceed previously reported 3D-printed FTEs by 10 to 100 times, bringing 3D-printed FTE performance on par with conventional materials.
Journal Article
Minimum mass-entransy dissipation profile for one-way isothermal diffusive mass-transfer process with mass-resistance and mass-leakage
As a new concept, mass-entransy is one of the twins in the core of entransy theory. It can describe mass-transfer ability for mass-transfer processes (MTPes), just as thermal-entransy for describing heat-transfer ability. Accordingly, mass-entransy dissipation can be utilized to evaluate the loss of mass-transfer ability. Minimum mass-entransy dissipation (MMED) is utilized to optimize one-way isothermal diffusive MTPes with mass-leakage and mass-transfer law (g ∝ Δ(
c
), where
c
means concentration). For a given net amount of mass-transferred key components at the low-concentration side, optimality-condition for the MMED of isothermal diffusive MTPes is obtained by using the averaged-optimization-method. Effects of the amount of mass-transferred and mass-leakage on optimal results are analyzed, and the obtained optimization profiles are compared with those for MTP profiles of constant-concentration-difference (
c
1
−
c
2
= const) and constant-concentration-ratio (
c
1
/
c
2
= const). The product of square of key-component-concentration (KCC) difference between high- and low-concentration sides and inert component concentration at high-concentration side for the MMED of the MTP with no mass-leakage is a constant, and the optimal relationship of the KCCs between high- and low-concentration sides with mass-leakage is significantly different from the former. When mass-leakage is relatively small, the MTP with
c
1
−
c
2
= const strategy is superior to that with
c
1
/
c
2
= const strategy, and the latter is superior to the former with an increase in mass-leakage. A combination of mass-entransy concept, finite-time thermodynamics, and averaged-optimization-method is a meaningful tool for optimizing MTPes.
Journal Article
A Review on Gas-Liquid Mass Transfer Coefficients in Packed-Bed Columns
This review provides a thorough analysis of the most famous mass transfer models for random and structured packed-bed columns used in absorption/stripping and distillation processes, providing a detailed description of the equations to calculate the mass transfer parameters, i.e., gas-side coefficient per unit surface ky [kmol·m−2·s−1], liquid-side coefficient per unit surface kx [kmol·m−2·s−1], interfacial packing area ae [m2·m−3], which constitute the ingredients to assess the mass transfer rate of packed-bed columns. The models have been reported in the original form provided by the authors together with the geometric and model fitting parameters published in several papers to allow their adaptation to packings different from those covered in the original papers. Although the work is focused on a collection of carefully described and ready-to-use equations, we have tried to underline the criticalities behind these models, which mostly rely on the assessment of fluid-dynamics parameters such as liquid film thickness, liquid hold-up and interfacial area, or the real liquid paths or any mal-distributions flow. To this end, the paper reviewed novel experimental and simulation approaches aimed to better describe the gas-liquid multiphase flow dynamics in packed-bed column, e.g., by using optical technologies (tomography) or CFD simulations. While the results of these studies may not be easily extended to full-scale columns, the improved estimation of the main fluid-dynamic parameters will provide a more accurate modelling correlation of liquid-gas mass transfer phenomena in packed columns.
Journal Article
Darcy-Forchheimer hybrid nanofluid flow over a stretching curved surface with heat and mass transfer
The present article provides a detailed analysis of the Darcy Forchheimer flow of hybrid nanoliquid past an exponentially extending curved surface. In the porous space, the viscous fluid is expressed by Darcy-Forchheimer. The cylindrical shaped carbon nanotubes (SWCNTs and MWCNTs) and Fe 3 O 4 (iron oxide) are used to synthesize hybrid nanofluid. At first, the appropriate similarity transformation is used to convert the modeled nonlinear coupled partial differential equations into nonlinear coupled ordinary differential equations. Then the resulting highly nonlinear coupled ordinary differential equations are analytically solved by the utilization of the “Homotopy analysis method” (HAM) method. The influence of sundry flow factors on velocity, temperature, and concentration profile are sketched and briefly discussed. The enhancement in both volume fraction parameter and curvature parameter k results in raises of the velocity profile. The uses of both Fe 3 O 4 and CNTs nanoparticles are expressively improving the thermophysical properties of the base fluid. Apart from this, the numerical values of some physical quantities such as skin friction coefficients, local Nusselt number, and Sherwood number for the variation of the values of pertinent parameters are displayed in tabular forms. The obtained results show that the hybrid nanofluid enhances the heat transfer rate 2.21%, 2.1%, and 2.3% using the MWCNTs, SWCNTs, and Fe 3 O 4 nanomaterials.
Journal Article
Biofilm growth in porous media well approximated by fractal multirate mass transfer with advective-diffusive solute exchange
Biofilm growth in porous media changes not only the hydrodynamic properties of the medium (reduction in porosity and permeability, and increase in dispersivity), but also the transport itself (breakthrough curves display increasingly fast first arrivals and long tails). These features are well reproduced by multicontinuum models (Multi‐Rate Mass Transfer, MRMT) which can be used to describe reactive transport in heterogeneous porous media and facilitate the simulation of reactions that are localized within biofilms. Here, we present a conceptual and numerical model of biochemical reactive transport with dynamic biofilm growth based on MRMT formulations. Mass exchange between mobile water and immobile biofilm aggregates is represented by a memory function, which simplifies definition of MRMT parameters. We successfully tested this model on two sets of laboratory data and found that (a) a basic model based on the growth of uniformly sized biofilm aggregates fails to reproduce laboratory tracer tests and rate of biofilm growth, while a fractal growth model, which we obtain by integrating the memory functions of biofilm aggregates with a power law distribution, does; (b) the biofilm memory function evolves as the biofilm grows; and (c) the early time portion of eluted volume tracer breakthrough curves are independent of flow rate, whereas the tail becomes heavier when the flow rate is decreased, which implies that both advection controlled and diffusion controlled mass exchange coexist in biofilms. These findings imply that porous media biofilms are essentially different from those developing in human tissues or open spaces. Key Points Biofilm aggregates with fractal size distributions are required for simulating growth and transport dynamics The evolution of anomalous transport during biofilm growth is well described by the fractal MRMT model Solute exchange between biofilm and mobile water is both advective and diffusive
Journal Article
Study the effect of different types impellers on the transfer coefficient in photobioreactor
In this research, study the effect of different types of impellers on the overall volumetric mass transfer coefficient, (determination of KLaO2 is very important for photobioreactor design and process analysis, Where through measuring KLaO2, the volumetric mass transfer coefficient of carbon dioxide is calculated based on the following relationship klaCO2 = 0.9 klaO2 Which is one of the most key factors that depend on it in the design of the photobioreactor )then make comparison between them, the impellers type which used in this research is 4-blade propeller, mixed flow impeller, 2-blade propeller(plastic), a hybrid photobioreactor type has been used in this research, which is a mixture of a bubble column and the stirred tank photobioreactor, The variables that studied in this research are the impeller speed (100-500) rpm, the rate of airflow into the reactor (1-4) L/min, and the type of impeller used. KLaO2 can be measured by static gassing out method. Through practical experiments, it was found that the highest value of KLaO2 in the 4 blade propeller was at a flow rate of 2 liters per minute and impeller speed 500 rpm, which equals 0.0091 (1 / s). As for the impeller (mixed flow impeller), the highest value of KLaO2 was at a speed of 500 rpm and a flow rate of 4 L / min which equals 0.0118 (1 / s). The highest value of KLaO2 in the impeller 2 blade propeller (plastic)) was at a flow rate of 4 liters per minute and impeller speed 500 rpm which was equal to 0.0101 (1 / s).A comparison is made between the three impellers on the basis of their efficiency in giving high values of KLaO2, where it was found that the mean value of the KLaO2 for the impeller (mixed flow impeller) is higher than the other impellers, where the average value of the KLaO2 at a speed of (100-500) rpm and the flow rate(1-4)L/min is 0.00806 (1 / s). This means that the type of impeller (mixed flow impeller) has a high efficiency of mixing and mass transfer between gas and liquid. In this study, correlation equations were developed for each impeller to see the correctness of the results according to specific exponents and constants within the range of previous studies and research, and it was found that theoretical volumetric mass transfer coefficient values are close to practical volumetric mass transfer coefficient values.
Journal Article
Power output and efficiency optimization of endoreversible non-isothermal chemical engine via Lewis analogy
Compared with endoreversible heat engine with pure heat transfer and endoreversible isothermal chemical engine with pure mass transfer, endoreversible non-isothermal chemical engine (ENICE) is a more reasonable model of practical mass exchanger, solid device and chemo-electric systems. There exists heat and mass transfer (HMT) simultaneously between working fluid and chemical potential reservoir in ENICE. There is coupled HMT effect that in ENICE should be considered. There are two ways to consider this coupled effect. One is based on Onsager equations, and another is based on Lewis analogy. For the mathematical and physical description of the above HMT process, the model using Onsager equations are more appropriate in the linear HMT region not far from the equilibrium state, while that based on Lewis analogy is more appropriate in nonlinear HMT region far from the equilibrium state. Different from the previous research on the power optimization of ENICEs with Onsager equations, this paper optimizes power and efficiency of ENICE based on Lewis analogy. HMT processes are assumed to obey Newtonian heat transfer law (
q
∝ Δ
T
, and
T
is temperature) and Fick’s diffusive mass transfer law (
g
∝ Δ
c
, and
c
is concentration), respectively. Analytical results of power output and corresponding vector efficiency (
η
T
and
η
μ
) of ENICE are obtained, which provide important parallel results with those based on Onsager equations. They include special cases for endoreversible Carnot heat engine with
q
∝ Δ
T
and endoreversible isothermal chemical engine with
g
∝ Δ
c
. Adopting Lewis analogy in the modelling of ENICEs with simultaneous HMT is an important work. It provides important analytical and numerical results different from those with Onsager equations obtained previously and enriches the research contents of FTT. The research results in this paper have a certain guiding significance for the optimal designs of single irreversible NICEs, multistage NICE systems, practical mass exchangers, solid devices, chemo-electric systems, and so on.
Journal Article